Field of the Invention
The invention relates to demodulators in bridge circuit configuration for frequency-modulated signals which comprise a parallel resonant circuit tuned to the carrier frequency of these signals and constituting one diagonal of the bridge circuit, the parallel resonant circuit being coupled to a signal source producing the signal to be demodulated via a primary winding. A second parallel circuit constitutes the other bridge diagonal and receives a voltage which is phase-shifted through 90.degree. relative to the voltage at the first parallel resonant circuit. Demodulators of this type are generally known as quotient demodulators, alternatively denoted as ratio detectors, or as phase demodulators. To generate the voltage to be coupled into the second bridge diagonal of such a demodulator it is customary to provide a further winding, alternatively designated the tertiary winding, which is strongly coupled, i.e. coupled with a relatively high coupling coefficient, to the primary winding of the first parallel resonant circuit, while a weak coupling is provided between the primary winding and the first parallel resonant circuit, as a result of which the desired 90.degree. phase shift is obtained between the voltage across the first parallel resonant circuit and the voltage coupled into the last mentioned bridge diagonal. Such a three-winding arrangement is comparatively expensive and the required, different coupling coefficients can only be implemented by the mechanical construction of the arrangement of the windings, so that the resultant coupling coefficients are comparatively tolerance-dependent and in the case of an inductive tuning of the parallel resonant circuit, which is the most customary way of tuning the resonant circuit, also dependent on the position of the ferromagnetic core within the windings, this position being variable for the purposes.